The present invention refers to a method for calibrating a camera-laser-unit with respect to at least one calibration-object disposed at a given position and orientation in a three-dimensional space. The camera-laser-unit comprises at least one laser (light-amplification by stimulated emission of radiation) and at least one camera. The laser and the camera are disposed in a given distance with respect to one another. An optical axis of the laser and an optical axis of the camera subtend a given angle. The camera-laser-unit is adapted to record the location, form and/or dimensions of a measurement-object.
The invention also concerns a calibration-object used for calibrating a camera-laser-unit and disposed at a given position and orientation within a three-dimensional space. The camera-laser-unit comprises at least one laser and at least one camera. The laser and the camera are disposed at a given distance and an optical axis of the laser and an optical axis of the camera subtend a given angle. The camera-laser-unit is adapted to record the location, form and/or dimensions of a measurement-object.
Camera-laser-units of the kind mentioned above are well known in the art. For example, such a camera-laser-unit is produced and sold by Perceptron, Inc., 47827 Halyard Drive, Plymouth, Mich. 48170, USA. Furthermore, such a camera-laser-unit and the use of such a unit is described in detail in the U.S. Pat. Nos. 4,645,348 and 6,166,811 both issued to Perceptron, Inc. A preferred embodiment of a camera-laser-unit of the kind mentioned above is described in detail in the German patent application 103 11 247, filed on Mar. 14, 2003 by the applicant of the present patent application. The publications of the two US-patents and of the German patent application are hereby incorporated by reference.
According to the methods known in the art, calibration of a camera-laser-unit is very complex and time-consuming. To begin with, a first calibration-object has to be disposed with respect to the camera-laser-unit and the camera is calibrated with respect to the first calibration-object by, for example, making use of a Tsai algorithm, which is well known in the art. Thereafter, a second calibration-object has to be disposed with respect to the camera-laser-unit and the laser is also calibrated with respect to the second calibration-object.
The second conventional calibration-object typically comprises a planar object with an array of pins protruding from the plane. The pins represent a non-coplanar calibration-pattern used for calibrating the laser. The dimensions and distances of the pins are known. The problem is that the pins, when illuminated by the laser or any other light source, form shadows on the adjacent pins, the shadows rendering very complicated and even impossible an accurate calibration of the laser.
Therefore, it is known to make the pins retractable and to extract them one by one from the planes of the cubic second calibration-object. After the extraction of each pin, a calibration routine is run and then the next pin is extracted with another calibration routine run thereafter, and so on. Thus, the calibration of the laser consists of numerous calibration routines. It may be well understood that in this way calibration of the laser is very cumbersome and requires a relatively long time. Typically, the calibration of the laser with the described method will take a couple of hours. Furthermore, the known calibration-method may be used only in laboratories or other places where the calibration assembly required for the calibration process may be built up. It is certainly not suited for calibration of lasers during the intended use of the camera-laser-unit.
One way for simplifying the calibration of the laser could be to reduce the number of pins. However, reducing the number of pins would reduce accuracy of the calibration.
It is an object of the present invention to simplify the process of calibration of a camera-laser-unit without reducing the associated accuracy.